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New Risk Assessment Approach for Systemic Insecticides: The Case of Honey Bees and Imidacloprid (Gaucho)

wo, 05/06/2009 - 19:19 — webmaster

Marie-Pierre Halm, A. Rortais, G. Arnold, J. N. Taséi, and S. Rault

Abstract

The procedure to assess the risk posed by systemic insecticides to honey bees follows the European Directives and depends on the determination of the Hazard Quotient (HQ), though this parameter is not adapted to these molecules. This paper describes a new approach to assess more specifically the risk posed by systemic insecticides to honey bees with the example of imidacloprid (Gaucho). This approach is based on the new and existing chemical substances Directive in which levels of exposure (PEC, Predicted Exposure Concentration) and toxicity (PNEC, Predicted No Effect Concentration) are compared. PECs are determined for different categories of honey bees in relation to the amounts of contaminated pollen and nectar they might consume. PNECs are calculated from data on acute, chronic, and sublethal toxicities of imidacloprid to honey bees, to which selected assessment factors are applied. Results highlight a risk for all categories of honey bees, in particular for hive bees. These data are discussed in the light of field observations made on honey bee mortalities and disappearances. New perspectives are given to better determine the risk posed by systemic insecticides to honey bees.

"The impact of systemic insecticides on honey bees is not limited to the impact of the parent compound; it also includes exposures to its metabolites. In the case of imidacloprid, some metabolites (e.g., olefin, which is twice more toxic than imidacloprid) are found to be very toxic to honey bees (9, 46, 47) and some of them are detected at low concentrations (between 0.3 and 1 µg/kg) in rape pollen and nectar (48).
However, to investigate in further detail the impact of metabolites on honey bees, their concentrations in other
types of pollen and nectar must be determined."

"To assess the risk posed to honey bees, chronic and sublethal toxicity tests must be conducted systematically, especially in the case of systemic insecticides which have a long-lasting action. To achieve these tests, standardized protocols are required and could be elaborated on the grounds of existing experimental studies which have investigated the chronic impacts of systemic insecticides on honey bees (9, 49, 50), as well as their sublethal effects on the behavior (41, 47, 51-53) and physiology (38, 54, 55) of these organisms."